Heating coil

A heating coil which is configured for heating concave and convex portions of a workpiece formed in a cylindrical shape, the concave and convex portions extending in a direction inclined with respect to a central axis of the workpiece and being formed on an outer peripheral surface of the workpiece, the heating coil comprising:

• a conductor portion configured to be disposed outside the workpiece, the conductor portion formed in a configuration so as to extend in a direction orthogonal to an inclination direction of the concave and convex portions formed on the outer peripheral surface of the workpiece, the outer peripheral surface of the workpiece having a circular shape when viewed in plan view with the workpiece received for heating by the heating coil, and the outer peripheral surface of the workpiece being parallel to the central axis of the workpiece, and
• the conductor portion having a facing surface configured on a part of the conductor portion facing the central axis of the workpiece and a non-facing surface configured on a part of the conductor portion where the conductor portion does not face the central axis of the workpiece;
• a first magnetic body configured to cover the non-facing surface of the conductor portion;
• and
• a second magnetic body set configured to be disposed adjacently to the first magnetic body,
• wherein the second magnetic body set is configured so that it covers a width of the non-facing surface and an upper outside portion of the facing surface and a lower outside portion of the facing surface, the second magnetic body set configured to be located at an upper side and a lower side outside of a portion of the conductor portion that faces the concave and convex portions, and
• the second magnetic body set is configured to expose the portion of the facing surface facing the concave and convex portions so that the facing surface has an area configured to be exposed to the workpiece between the upper outside portion and the lower outside portion.